Arthrodesis devices for generating and applying compression within joints

ABSTRACT

Arthrodesis devices and arthrodesis procedures are disclosed herein. In an embodiment, an arthrodesis device includes a shape memory material connecting member attached to two points of fixation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims priority to U.S. Provisional Application No.62/322,847, filed on Apr. 15, 2016, and claims priority to U.S.Provisional Application No. 62/412,021, filed on Oct. 24, 2016.

The entire disclosures of each of the above priority applications areincorporated herein by reference.

BACKGROUND

This disclosure relates to intramedullary devices, and more particularlyto arthrodesis (i.e., fusion) devices for generating and applyingcompression within a joint.

Arthrodesis procedures are common in the field of orthopedic surgery forrepairing arthritic and deteriorated bones. The success of thesesurgical procedures often depends on the successful approximation ofbone and on the amount of compression achieved between the bones.

Intramedullary devices can be used during arthrodesis procedures. Thesedevices are designed to reduce and create a compressive load betweenbones. However, known intramedullary devices do not always achieve thisgoal. It would therefore be useful if intramedullary devices wereavailable that generate and maintain a compressive load within a jointwhile bone healing occurs.

SUMMARY

This disclosure relates to arthrodesis devices, such as intramedullarynails, for performing arthrodesis or fusion procedures within human oranimal bodies.

The arthrodesis devices described herein may be capable of bringingbones or bone fragments in proximity to one another, generating acompressive load, and maintaining the compressive load for a prolongedperiod of time while healing occurs.

An arthrodesis device includes, inter alia, a nail body extending alonga longitudinal axis between a proximal portion and a distal portion. Aproximal slider is housed inside the proximal portion, and a distalslider is housed inside the distal portion. A shape memory material rodis connected to both the proximal slider and the distal slider. A cableis connected to the distal slide. The cable may be tensioned to move thedistal slider inside the nail body and thereby stretch the shape memorymaterial rod.

Another arthrodesis device includes, inter alia, a nail body extendingalong a longitudinal axis between a proximal portion and a distalportion, a proximal interlocking fixation body located inside or outsidethe proximal portion, a distal interlocking fixation body located insideor outside the distal portion, and a shape memory material connectingmember attached to the proximal interlocking fixation body and thedistal interlocking fixation body.

A method for performing an arthrodesis procedure includes, inter alia,inserting an arthrodesis device within a joint, inserting a firstfixation device through the arthrodesis device, inserting a secondfixation device through the arthrodesis device, tensioning a cable ofthe arthrodesis device such that the cable alters a shape memorymaterial connecting member of the arthrodesis device from an unstretchedcondition to a stretched condition, and releasing tension on the cable.Releasing tension on the cable causes the shape memory materialconnecting member to move back toward the unstretched condition, therebyapplying a compressive load across bones of the joint.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a joint of the human musculoskeletal system.

FIG. 2 illustrates an arthrodesis device for performing arthrodesisprocedures.

FIG. 3 is a front view of the arthrodesis device of FIG. 2.

FIG. 4 is a top view of the arthrodesis device of FIG. 2.

FIG. 5 is a cross-sectional view taken through section A-A of FIG. 4.

FIG. 6A illustrates a proximal interlocking fixation body of thearthrodesis device of FIG. 2.

FIG. 6B illustrates a distal interlocking fixation body of thearthrodesis device of FIG. 2.

FIG. 7 illustrates a shape memory material connecting member of thearthrodesis device of FIG. 2.

FIG. 8 schematically illustrates an exemplary method for performing anarthrodesis procedure.

FIG. 9 illustrates another exemplary arthrodesis device.

FIG. 10 illustrates a shape memory material connecting member of thearthrodesis device of FIG. 9.

FIG. 11 illustrates stretched and unstretched conditions of a shapememory material connecting member of an arthrodesis device.

FIG. 12 illustrates a channel for receiving the shape memory materialconnecting member of FIG. 11.

FIG. 13 illustrates another exemplary arthrodesis device.

FIG. 14 illustrates another exemplary arthrodesis device, shown bothbefore and during the application of dynamic compression.

FIG. 15 illustrates yet another exemplary arthrodesis device.

FIG. 16 illustrates another exemplary arthrodesis device.

FIG. 17 illustrates another exemplary arthrodesis device.

FIG. 18 illustrates another exemplary arthrodesis device.

FIG. 19 illustrates yet another exemplary arthrodesis device.

FIG. 20 illustrates exemplary end caps for an arthrodesis device.

FIG. 21 illustrates additional exemplary end caps for an arthrodesisdevice.

DETAILED DESCRIPTION

This disclosure describes exemplary arthrodesis devices, such asintramedullary nails, for performing arthrodesis or fusion procedureswithin human or animal bodies. The arthrodesis devices described by thisdisclosure are capable of bringing bones or bone fragments in proximityto one another, generating a compressive load, and maintaining thecompressive load for a prolonged period of time while healing occurs.

An arthrodesis device includes, inter alia, a nail body extending alonga longitudinal axis between a proximal portion and a distal portion. Aproximal slider is housed inside the proximal portion, and a distalslider is housed inside the distal portion. A shape memory material rodis connected to both the proximal slider and the distal slider. A cableis connected to the distal slide. The cable may be tensioned to move thedistal slider inside the nail body and thereby stretch the shape memorymaterial rod.

Another arthrodesis device includes, inter alia, a nail body extendingalong a longitudinal axis between a proximal portion and a distalportion, a proximal interlocking fixation body located inside or outsidethe proximal portion, a distal interlocking fixation body located insideor outside the distal portion, and a shape memory material connectingmember attached to the proximal interlocking fixation body and thedistal interlocking fixation body.

In a further embodiment, a nail body of an arthrodesis device includesat least one opening configured to receive a fixation device, such as ascrew, peg, etc.

In a further embodiment, a proximal interlocking fixation body islocated inside a proximal portion of a nail body and a distalinterlocking fixation body is located inside a distal portion of thenail body.

In a further embodiment, a proximal interlocking fixation body islocated outside a proximal portion of a nail body and a distalinterlocking fixation body is located outside a distal portion of thenail body

In a further embodiment, a first opening of a nail body of anarthrodesis device is located within a proximal portion of the nail bodyand receives a tibial screw, a second opening is located within a distalportion of the nail body and receives a talar screw, and a third openingis located within the distal portion of the nail body and receives acalcaneal screw.

In a further embodiment, a shape memory material connecting member of anarthrodesis device is a rod made of Nitinol (NiTi).

In a further embodiment, a shape memory material connecting member of anarthrodesis device includes an elongated shaft extending between a firstthreaded portion and a second threaded portion.

In a further embodiment, a first threaded portion of a shape memorymaterial connecting member of an arthrodesis device is received within afirst threaded opening of a proximal interlocking fixation body, and asecond threaded portion is received within a second threaded opening ofa distal interlocking fixation body. Thereby, a shape memory materialconnecting member (e.g., nitinol) is attached to at least two points offixation (e.g., fixation devices received through proximal and distalinterlocking fixation bodies).

In a further embodiment, a distal interlocking fixation body of anarthrodesis device is translatable within a cannulation of a nail body.

In a further embodiment, a cable of an arthrodesis device is connectedto a distal interlocking fixation body. The cable is tensioned to movethe distal interlocking fixation body inside a nail body.

In a further embodiment, when a nail body of an arthrodesis device isimplanted, a shape memory material connecting member is movable betweenan unstretched position and a stretched position to generate acompressive force across bones of a joint.

A method for performing an arthrodesis procedure includes, inter alia,inserting an arthrodesis device within a joint, inserting a firstfixation device through the arthrodesis device, inserting a secondfixation device through the arthrodesis device, tensioning a cable ofthe arthrodesis device such that the cable alters a shape memorymaterial connecting member of the arthrodesis device from an unstretchedcondition to a stretched condition, and releasing tension on the cable.Releasing tension on the cable causes the shape memory materialconnecting member to move back toward the unstretched condition, therebyapplying a compressive load across bones of the joint.

In a further embodiment, a joint that is repaired during an arthrodesisprocedure is a tibio-talo-calcaneal (TTC) joint of an ankle.

In a further embodiment, a method includes, prior to inserting anarthrodesis device, inserting a guide wire into a joint, and reaming apassage through the joint for accommodating the arthrodesis device.

In a further embodiment, a first fixation device is a most distalcalcaneal screw tibial screw and a second fixation device is a tibialscrew through a proximal interlocking fixation body.

In a further embodiment, a method includes inserting a third fixationdevice through an arthrodesis device after inserting a second fixationdevice. The third fixation device is either a talar screw or a calcanealscrew.

In a further embodiment, a shape memory material connecting memberconnects between a proximal interlocking fixation body and a distalinterlocking fixation body of an arthrodesis device and a cable isconnected to the distal interlocking fixation body. The cable istensioned to translate the distal interlocking fixation body in aproximal to distal direction.

In a further embodiment, translating a distal interlocking fixation bodymoves a shape memory material connecting member of an arthrodesis devicefrom an unstretched condition to a stretched condition.

In a further embodiment, a proximal interlocking fixation body is fixedfrom movement prior to tensioning a cable.

In a further embodiment, inserting a third fixation device substantiallylocks a positioning of a distal interlocking fixation body of anarthrodesis device.

In a further embodiment, a third fixation device is a calcaneal screw.

FIG. 1 schematically illustrates a joint 10 of the human musculoskeletalsystem that has been repaired using an arthrodesis device 12. In anembodiment, the arthrodesis device 12 is specifically configured for usewith a tibio-talo-calcaneal (TTC) joint of an ankle. However, thearthrodesis devices 12 of this disclosure could be used to repair otherjoints within the scope of this disclosure (e.g., femoral, humeral,tibial, etc.).

The joint 10 includes a calcaneus 14, a talus 16, and a tibia 18. Thejoint 10 may become unstable if there is significant cartilage lossand/or diseased bone at the articulating surfaces 19 of the calcaneus14, the talus 16, and/or the tibia 18. Over time, the patient sufferingfrom this instability can develop arthritis, thus resulting insignificant pain.

This disclosure describes arthrodesis devices for fusing such unstablejoints. Fusing the bones of the joint 10 together causes the calcaneus14, the talus 16, and the tibia 18 to act as a single bone, thussubstantially eliminating motion and reducing pain caused by thearthritic joint. Although TTC joint fusions of the ankle are describedthroughout this disclosure as one example arthrodesis technique, thisdisclosure is not intended to be limited to only TTC joint fusions.

FIGS. 2, 3, 4, and 5 illustrate an exemplary arthrodesis device 12according to a first embodiment of this disclosure. The arthrodesisdevice 12 includes a nail body 20 that extends along a longitudinal axisA between a proximal portion 22 and a distal portion 24. In anembodiment, the arthrodesis device 12 is configured such that once thearthrodesis device 12 has been implanted within the joint 10 of FIG. 1,the proximal portion 22 of the nail body 20 extends into the tibia 18 ofthe joint 10, and the distal portion 24 of the nail body 20 extends intoboth the calcaneus 14 and the talus 16 of the joint 10 (see, e.g., FIG.1).

The nail body 20 is configured as a sleeve for housing other componentsof the arthrodesis device 12 (discussed further below). In anembodiment, the nail body 20 may be made of a titanium alloy, such asTi-6Al-4V. However, other materials are also contemplated within thescope of this disclosure.

The nail body 20 includes multiple openings for receiving fixationdevices, such as screws, pegs, etc., for fixating the arthrodesis device12 within the joint 10. For example, the proximal portion 22 of the nailbody 20 may include a first proximal opening 26 and a second proximalopening 28 that is slightly distal (i.e., displaced in a directiontoward the distal portion 24) to the first proximal opening 26. Each ofthe first proximal opening 26 and the second proximal opening 28 mayreceive a tibial screw 30 for fixating the arthrodesis device 12 to thetibia 18. In an embodiment, the first proximal opening 26 is a roundopening and the second proximal opening 28 is an elongated slot. Inanother embodiment, the first proximal opening 26 and the secondproximal opening 28 extend through opposing side surfaces 42 of the nailbody 20, which may extend at a perpendicular angle relative to thelongitudinal axis A (see, e.g., FIG. 2 and side view of FIG. 3).

The distal portion 24 of the nail body 20 may include a first distalopening 32, a second distal opening 34, and a third distal opening 36.The second distal opening 34 may be just proximal of the first distalopening 32 (i.e., displaced in a direction toward the proximal portion22), and the third distal opening 36 may be just proximal to the seconddistal opening 34. The first and second distal openings 32, 34 may eachreceive a calcaneal screw 38 for fixating the arthrodesis device 12 tothe calcaneus 14, and the third distal opening 36 may receive a talarscrew 40 for fixating the arthrodesis device 12 to the talus 16. In anembodiment, the first distal opening 32 is a round opening and thesecond and third distal openings 34, 36 are elongated slots. In anotherembodiment, the first and second distal openings 32, 34 extend through atop surface 44 and a bottom surface 46 of the nail body 20, and mayextend at a perpendicular angle relative to the longitudinal axis A(see, e.g., FIG. 2 and top view of FIG. 4). The third distal opening 36extends through the opposing side surface 42 of the nail body 20, andmay extend at a perpendicular angle relative to the longitudinal axis A(see, e.g., FIG. 2 and top view of FIG. 4). The first proximal opening26, the second proximal opening 28, and the third distal opening 36 maytherefore extend in parallel with one another. Further, the first andsecond distal openings 32, 34 may extend perpendicular to the firstproximal opening 26, the second proximal opening 28, and the thirddistal opening 36.

As best illustrated by the cross-sectional view of FIG. 5, the nail body20 of the arthrodesis device 12 may house a proximal interlockingfixation body 48, a distal interlocking fixation body 50, and a shapememory material connecting member 52. The proximal interlocking fixationbody 48 is slidably received within a first cannulation 54 of the nailbody 20 and is at least partially exposed within the second proximalopening 28, the distal interlocking fixation body 50 is slidablyreceived within a second cannulation 56 of the nail body 20 and is atleast partially exposed within the second and third distal openings 34,36, and the shape memory material connecting member 52 is receivedwithin a third cannulation 58 of the nail body 20 and is connected(e.g., threadably engaged) to both the proximal interlocking fixationbody 48 and the distal interlocking fixation body 50. In an embodiment,the proximal interlocking fixation body 48 and the distal interlockingfixation body 50 act as sliders that move inside the nail body 20.

In an embodiment, the proximal interlocking fixation body 48 and thedistal interlocking fixation body 50 are made of a titanium alloy, suchas Ti-6Al-4V. In another embodiment, the proximal interlocking fixationbody 48 and the distal interlocking fixation body 50 are proximal anddistal sliders, respectively, of the arthrodesis device 12.

In another embodiment, the shape memory material connecting member 52may be configured as a rod, e.g., a rod made of Nitinol (NiTi). However,the shape memory material connecting member 52 could have other shapesand configurations, and other superelastic materials (e.g., materialscapable of exhibiting superelasticity and/or a temperature-induced shapechanges) can be used to construct the shape memory material connectingmember 52.

The arthrodesis device 12 additionally includes a cable 60, which may beused as a tensioning device as will be described. The cable 60 isattached to the distal interlocking fixation body 50 and extends to alocation outside of the nail body 20. In an embodiment, the cable 60 ismade of stainless steel, such as 304V Stainless Steel.

In use, the cable 60 may be tensioned to move the distal interlockingfixation body 50 within the second cannulation 56, thereby stretchingthe shape memory material connecting member 52 to a stretched position.Once stretched, the superelasticity of the shape memory materialconnecting member 52 causes it to want to return toward its unstretchedposition. The arthrodesis device 12 can therefore apply a constantcompression force across the bones of the joint 10 once fixated withinthe joint 10.

FIGS. 6A and 6B illustrate additional features of the proximalinterlocking fixation body 48 and the distal interlocking fixation body50, respectively. Referring first to FIG. 6A, the proximal interlockingfixation body 48 includes a threaded opening 62 extending along a firstaxis A1 and a non-threaded opening 64 extending along a second axis A2.In an embodiment, the second axis A2 is perpendicular to the first axisA1. The threaded opening 62 may receive a portion of the shape memorymaterial connecting member 52 (see FIG. 5), and the non-threaded opening64 may receive a tibial screw 30 (see FIG. 2). A second non-threadedopening 65 may extend along a third axis A3 that is parallel to thesecond axis A2. The second non-threaded opening 65 may receive a pin,such as a PLLA pin, that can be press fit into place so the proximalinterlocking fixation body 48 does not move before tensioning the cable60.

Referring now to FIG. 6B, the distal interlocking fixation body 50includes a threaded opening 66 extending along a first axis A1, a firstnon-threaded opening 68 extending along a second axis A2, a secondnon-threaded opening 70 extending along a third axis A3, and a thirdnon-threaded opening 72 extending along a fourth axis A4. In anembodiment, the second axis A2, the third axis A3, and the fourth axisA4 are each perpendicular to the first axis A1. In another embodiment,the second and fourth axes A2, A4 are parallel to one another butperpendicular to the third axis A3. The threaded opening 66 may receivea portion of the shape memory material connecting member 52 (see FIG.5), the first non-threaded opening 68 may receive a talar screw 40 thatextends through the third distal opening 36 of the nail body 20 (seeFIG. 2), the second non-threaded opening 70 may receive a calcanealscrew 38 that extends through the second distal opening 34 of the nailbody 20 (see FIG. 2), and the third non-threaded opening 70 may receivethe cable 60 of the arthrodesis device 12 (see FIG. 5).

FIG. 7 illustrates additional features of the shape memory materialconnecting member 52. The shape memory material connecting member 52 mayinclude an elongated body 74 having a first threaded portion 76, asecond threaded portion 78, and a shaft 80 extending between the firstthreaded portion 76 and the second threaded portion 78. In anembodiment, the first threaded portion 76 and the second threadedportion 78 include a second diameter D2 that is larger than a firstdiameter D1 of the shaft 80. The first threaded portion 76 may engagethe threaded opening 62 of the proximal interlocking fixation body 48and the second threaded portion 78 may engage the threaded opening 66 ofthe distal interlocking fixation body 50 to connect the shape memorymaterial connecting member 52 to each of the proximal and distalinterlocking fixation bodies 48, 50 (see FIG. 5). The shaft 80 may bedisposed within the third cannulation 58 of the nail body 20.

FIG. 8, with continued reference to FIGS. 1-7, schematically illustratesa method 82 for performing an arthrodesis procedure. The method 82 isdescribed for using the arthrodesis device 12 to fuse together the bonesof the joint 10 shown in FIG. 1. However, other joints could be repairedusing a similar procedure as the one described below. It should beappreciated that features of the arthrodesis device 12 may bespecifically configured in order to provide the method 82 described. Itshould further be understood that the method 82 described could includea greater or fewer number of steps and that the steps could be performedin a different order within the scope of this disclosure.

The method 82 begins at block 84 by removing any remaining cartilage andperforming any necessary osteotomies to remove diseased bone and exposethe subchondral bone of the calcaneus 14, the talus 16, and the tibia18. This step creates the necessary surface areas for fusing thecalcaneus 14, the talus 16, and the tibia 18 together.

Next, as schematically illustrated at block 86, a guide wire is placedso it extends through the calcaneus 14 and the talus 16 and extendspartially into the tibia 18. The guide wire is drilled into the joint 10in an inferior-to-superior direction (i.e., entering through inferiorside of calcaneus 14, and then through talus 16 and into tibia 18). Apassage is then reamed into the joint 10 at block 88 for accommodatingthe arthrodesis device 12. A reamer may be inserted over the guide wireto ream the passage.

The arthrodesis device 12 is inserted into the reamed passage at block90. Placement of the arthrodesis device 12 may be guided by a targetingdevice (not shown). Insertion of the arthrodesis device 12 may requirelight tapping to insert the arthrodesis device 12 at the proper distancewithin the tibia 18.

A calcaneal screw 38 is inserted through the first distal opening 32 ofthe nail body 20 at block 91 to affix the arthrodesis device 12 inplace. Then, at block 92, a tibial screw 30 is inserted through thesecond proximal opening 28 of the nail body 20 and through thenon-threaded opening 64 of the proximal interlocking fixation body 48.Insertion of the tibial screw 30 in this manner substantially locks theproximal interlocking fixation body 48 from further movement relative tothe nail body 20.

The cable 60 is tensioned at block 93. The cable 60 may be tensionedusing a suitable tensioning device (not shown). Tensioning the cable 60moves (e.g., slides) the distal interlocking fixation body 50 distallywithin the third distal opening 36. The distal interlocking fixationbody 50 may therefore operate as a slider inside the nail body 20. Sincethe proximal interlocking fixation body 48 is now fixed, this movementstretches the shape memory material connecting member 52 to generate acompressive load. The tension is held on the cable 60 while a talarscrew 40 is inserted through the third distal opening 36 of the nailbody 20 and through the first non-threaded opening 68 of the distalinterlocking fixation body 50 at block 94. A second calcaneal screw 38is inserted through the second distal opening 34 of the nail body 20 andthrough the second non-threaded opening 70 of the distal interlockingfixation body 50 at block 95.

Tension may then be released from the cable 60 at block 96. The cable 60is then removed. Releasing the tension on the cable 60 causes the shapememory material connecting member 52 to attempt to recover the straincaused by stretching the shape memory material connecting member 52 tothe stretched position, thus creating and maintaining a compressiveforce across the bones of the joint 10.

The method 82 may conclude at block 97 by inserting a second tibialscrew 30 through the first proximal opening 26 of the nail body 20. Thisstep may optionally be performed and is based on the surgeon'sdiscretion.

Additional embodiments of this disclosure include the provision and useof arthrodesis devices configured as compression intramedullary (IM)nails, which may be manufactured from Titanium, stainless steel, or thelike. Those IM nails may include shape memory materials (e.g., materialscapable of exhibiting superelasticity and/or a temperature-induced shapechange), which either pull or push locking screws together, and therebyeffectively pulling or pushing bone fragments together. It should beappreciated that features of the following examples may also be usedwith the arthrodesis devices 12 described above

FIG. 9 illustrates one such exemplary IM nail 100. In an embodiment,locking screws 102, 103 are interconnected to one another (e.g., insidethe bore of the IM nail 100) with a shape memory material connectingmember 104, such as a superelastic Nitinol wire, rod (see, e.g., FIG.10), tube or ribbon. The shape memory material connecting member 104 maybe considered to be similar in nature to a tie. Once the proximallocking screw 102 is locked into its round hole 106, the distal lockingscrew 103 is placed at the bottom or distal end of an oblong dynamicslot 108 that is located furthest from the proximal end. The IM nail 100may be delivered with the shape memory material connecting member 104stretched superelastically between the proximal and distal lockingscrews 102, 103 and is held in the stretched or lengthened condition.Once the locking screws 102, 103 are placed, the shape memory materialconnecting member 104 is unconstrained and allowed to foreshorten, thuspulling the locking screws 102, 103 together like a tie-rod andeffectively pulling the bones together across a fracture site FS. Thismay reduce the fracture, stabilize the bones, and apply sustained,non-linear compression to the fracture site FS. The shape memorymaterial connecting member 104 may be pre-strained in the IM nail 100before insertion into the IM space and may be released once in place andthe locking screws 102, 103 are cross-threaded into place to secure theIM nail 100.

Throughout this description, the shape memory material of the shapememory material connecting member 52, 104 may be a metal alloy (e.g.,Nitinol) or an elastic polymer (e.g., appropriately processed PEEK). Thecompression IM nail 100 is designed to engage and stabilize bonefragments and to generate compression between the bone fragments. IfNitinol is used, the shape memory material connecting member 104 may beconstrained in the “cold” condition. In doing so, this may takeconsiderably less force to strain the non-austenitic form of the shapememory material. The load that is required to stretch martensiticNitinol may be less than half that required to stress the material inits austenitic phase. It is possible to stretch the Nitinol up to 8%strain along the material's Upper Plateau, unload 2% strain allowing therecoverable force to decrease by almost 50% to the materials LowerPlateau, so when it is finally unconstrained and allowed to recover thebalance of the 6% strain it does so on the lower plateau so the force ittoo great that it damages the interlocking screws 102, 103 or the bonethat the screws 102, 103 are inserted into.

Furthermore, the surface finish of the shape memory material connectingmember 104 effects its biocompatibility and fatigue life. Prior tostraining, the shape memory material connecting member 104 may bepassivated to remove embedded surface contaminants that may haveresulted from the manufacturing process. Passivation also creates abiocompatible oxide layer on the surface of Nitinol. Straining theNitinol shape memory material connecting member 104 with a high load(i.e., the type of high load required to stress the Nitinol in anaustenitic phase) can damage this biocompatible oxide layer, and canembed particles into its surface. Lower loads (i.e., the type of loadsrequired to stress the compression screw in a non-austenitic phase) willminimize any damage to the surface finish.

With the Nitinol shape memory material connecting member 104 “cold”(i.e., maintained below its austenite start temperature, more preferablybelow its martensite start temperature, and most preferably below itsmartensite finish temperature) and strained (i.e., stretched), the shapememory material connecting member 104 is installed to constrain thedistal locking screw 103 from shortening and migrating to the proximalend of the oblong dynamic slot 108. More particularly, with the Nitinolshape memory material connecting member 104 maintained below itsaustenite start temperature, the ends of the stretched Nitinol arethreaded to the ends caps of the IM nail 100 to keep the materialstretched. The Nitinol shape memory material connecting member 104 canthen be warmed above its austenite start temperature and it will notforeshorten due to the presence of threaded ends caps 110 retaining theNitinol shape memory material connecting member 104 in the stretched,constrained martensite.

However, when the end caps 110 are unthreaded and released, the shapememory material connecting member 104 will attempt to revert back to itsnon-strained (i.e., unstretched) length, i.e., the Nitinol member willattempt to foreshorten and the compressive force generated by thestrained superelastic material which is trying to foreshorten putssustained compression on the interlocking screws 102, 103, strain in theoblong dynamization slots 108 and put sustained, compressive loads onthe fracture site FS.

Note that the Nitinol shape memory material connecting member 104 isconfigured so that the force that is generated by the materialforeshortening is less than the strength of the locking screws 102, 103,so that compression does not bend or break the locking screws 102, 103when attempting to foreshorten. Additionally the Nitinol shape memorymaterial connecting member 104 is specifically engineered so not toapply too much force to the bones so aggressively that the screws 102,103 “tear through” the bone tissue. The compressive forces of the shapememory material connecting member 104 can be controlled by modulatingthe material properties and/or the geometry of the shape memory materialconnecting member 104.

The percentage of cold work in the shape memory material connectingmember 104 can affect the compressive force generated by the device 104.As the percentage of cold work increases, the compression forcedeclines. In an embodiment, the shape memory material connecting member104 includes between about 15% and 55% cold work to control the recoveryforce of the Nitinol shape memory material connecting member 104.

Another material property that affects the compression force of theshape memory material connecting member 104 is the temperaturedifferential between the body that the compression screw will beimplanted into (assumed to be 37° C., which is the temperature of ahuman body) and the austenite finish temperature of the shape memorymaterial connecting member 104. A smaller temperature differentialbetween the two will result in the Nitinol shape memory materialconnecting member 104 generating a small compressive load; conversely,the larger the temperature differential between the two will result in aNitinol connecting member generating a larger compressive load. In anembodiment, the shape memory material that the shape memory materialconnecting member 104 is made out of includes an austenite finishtemperature of greater than about 10° C. This may result in atemperature differential of less than about 47° C. when the shape memorymaterial connecting member 104 is implanted in a human body.

The geometry of the shape memory material connecting member 104 alsoaffects the compression force that is ultimately generated. Thecross-sectional area of the shape memory material connecting member 104affects the compression force. As the cross-sectional area increases, sodoes the compression force that the shape memory material connectingmember 104 will generate. In this respect, it should be appreciated thatit is beneficial for the compression force generated by foreshorteningthe shape memory material connecting member 104 to be constant as thebone relaxes and remodels. Thus, in an embodiment, the cross-section ofthe shape memory material connecting member 104 may have a constantcross-section over its entire length. Cross-sections that are notuniform over the length of the shape memory material connecting member104 can result in an increase or decrease in compression as the shapememory material connecting member 104 shortens.

In another embodiment, the shape memory material connecting member 104is stretched while it is at a temperature below its austenite starttemperature, and with the end caps 110 threading the shape memorymaterial connecting member 104 in the stretched condition, below itsaustenite start temperature. However, if desired, the shape memorymaterial connecting member 104 may be stretched while it is at atemperature above its austenite start temperature, whereby to createstress-induced martensite.

In another embodiment, the shape memory material connecting member 104of the IM nail 100 is cannulated and provided in the form of asterilized kit. The kit may include additional instruments to aid in theimplantation of the IM nail 100 (e.g., k-wire, drill bit, screw sizeguide, etc.).

TTC ankle fusion is a technique that may be used to achieve functional,stable, and pain-free orthopedic fusion for the treatment of appropriatemedical conditions. Intentional bone fusions which are oftenunsuccessful can lead to patient pain, recurring surgery, infection,loss of limb function, and/or, in extreme cases, limb amputation. IMnails that can provide sustained compressive forces across a bone fusionsite despite bone resorption processes are desired. By connecting andpulling the locking screws 102, 103 together, the IM nail 100 mayprovide sustained, compression to the fracture site.

FIGS. 11 and 12 illustrate another exemplary IM nail 200. The IM nail200 includes a shape memory material connecting member 204 that can belocated on the outside of the IM nail 200 (see FIG. 11), or couldinclude a combination of both outer and inner shape memory materialconnecting members 204. The shape memory material connecting member 204can be recessed into a channel 212 (e.g., a milled channel) or flute inthe outer diameter of the IM nail 200. In such an embodiment, the shapememory material connecting member 204 may not sit proud of the diameter(see, e.g., FIG. 12).

FIG. 13 illustrates another exemplary IM Nail 300. In an embodiment,interconnecting locking screws 302, 303 can be forced together by usingone or more springs 314. The springs 314 can be made of variousmaterials, including but not limited to, stainless steel, Titanium,cobalt-chrome, MP35N, Nitinol, L605, and various other biocompatiblealloys.

There can be one or multiple springs 314 used to push theinterconnecting locking screws 302, 303 together so long as there is atleast one slot for the screw to axially travel in. In an embodiment, thescrew 302 that is being pushed along its slot 308 is applying sustainedcompression to a fracture site. The springs 314 can be positionedbetween end caps 310 of the IM nail 300 and the locking screws 302, 303so that the springs 314 push the locking screws 302, 303 toward afracture site. Alternatively, the springs 314 can be part of a set-screwpositioned just distal the end cap but proximal to the interconnectinglocking screw 302 in the dynamization slot 308. It is possible to use acoil spring, wave spring, or die set spring; or a combination thereof.The spring 314 can be made of MP35N, Titanium alloys, Elgiloy, CobaltChrome alloys, and various other biocompatible alloys.

FIG. 14 illustrates yet another exemplary IM nail 400. The IM nail 400may be a TTC fusion nail having a spring 414 and a tuning fork device416 which can be inserted into the IM nail 400 to push or compress thespring 414, thus allowing access or passage of the interconnectinglocking screws 402, 403 thru the IM nail 400. Once the interconnectingscrews 402, 403 are threaded in place, the tuning fork device 416 may beremoved by pulling out the open end. The spring 414 may then be allowedto expand and apply a force against the screw 402 in the dynamizationslot 408.

FIG. 15 illustrates yet another IM nail 500, which may be aCephalomedullary IM nail, for example. In this embodiment, springs 514apply compression to interconnecting screws 502, 503 to create sustainedcompression. The springs 514 can compress against the screws 502, 503themselves, or may compress against a device that cradles or nests thescrews 502, 503.

FIG. 16 illustrates another IM nail 600. The IM nail 600 may include atuning fork device 616 that compresses a spring 614 allowing passage ofa screw 602, 603 through the IM nail 600 (see inset I-1). The tuningfork device 616 may be released off the spring 614 to expand the spring614 (see inset I-2), thus pushing the IM nail 600 proximally and loadingthe fracture site FS.

FIGS. 17-21 illustrate yet another exemplary IM nail 700. The IM nail700 may include end caps 710 that thread into openings 718 of the IMnail 700. The end caps 710 may be static and may thread against a staticset-screw 720. A spring 714 may be positioned within the end cap 710(see inset I-2), thus rendering it dynamic. The end cap 710 can bethreaded and designed to look more like a spring plunger. The end cap710 can include an internal thread which pushes a plunger 722 against aninterconnecting screw 702 that may be placed through an oblong,dynamization slot 708 (see FIG. 17).

The dynamic end caps 710 can be used in all types of IM nails and sucharthrodesis devices. FIG. 18 illustrates their use in a femoral nail,and FIG. 19 illustrates their use for an ankle nail.

It is also possible to pull the screws 702, 703 together with a Nitinolconnecting member 704 while also using springs 714 to push theinterconnecting locking screws 702, 703 together. This may maximize thesustained compression (see, e.g., FIG. 20). The connecting member 704can be a wire or cable with welded bead ends or swaged end fittings 724(see, e.g., FIG. 21). The end caps 710 can accept a compression screw orspring and can be swaged or welded to the connecting member 704.

This disclosure provides novel arthrodesis devices capable of bringingbone or bone fragments into close proximity with each other, generatinga compressive load, and maintaining the compressive load for a prolongedperiod of time while healing occurs.

Although the different non-limiting embodiments are illustrated ashaving specific components or steps, the embodiments of this disclosureare not limited to those particular combinations. It is possible to usesome of the components or features from any of the non-limitingembodiments in combination with features or components from any of theother non-limiting embodiments.

It should be understood that like reference numerals identifycorresponding or similar elements throughout the several drawings. Itshould further be understood that although a particular componentarrangement is disclosed and illustrated in these exemplary embodiments,other arrangements could also benefit from the teachings of thisdisclosure.

The foregoing description shall be interpreted as illustrative and notin any limiting sense. A worker of ordinary skill in the art wouldunderstand that certain modifications could come within the scope ofthis disclosure. For these reasons, the following claims should bestudied to determine the true scope and content of this disclosure.

What is claimed is:
 1. An arthrodesis device for performingtibio-talo-calcaneal (TTC) joint fusions, comprising: a nail bodyextending along a longitudinal axis between a proximal portion and adistal portion; a proximal slider housed inside the proximal portion; adistal slider housed inside the distal portion; a Nitinol rod connectedto both the proximal slider and the distal slider; a first openinglocated within the proximal portion of the nail body and configured toreceive a tibial screw; a second opening located within the distalportion of the nail body and configured to receive a talar screw; athird opening located within the distal portion of the nail body andconfigured to receive a calcaneal screw, wherein at least one of thefirst opening, the second opening, and the third opening is an elongatedslot; and a cable connected to the distal slider; wherein the cable istensionable to move the distal slider inside the nail body and therebystretch the Nitinol rod.
 2. The device as recited in claim 1, whereinthe cable is looped through a non-threaded opening of the distal slider.3. The device as recited in claim 2, wherein the non-threaded opening isdistal of the talar screw and the calcaneal screw.
 4. The device asrecited in claim 1, wherein the distal slider includes at least threenon-threaded openings and the proximal slider includes at least twonon-threaded openings.
 5. The device as recited in claim 4, wherein thecable is looped through a distal most opening of the at least threenon-threaded openings.
 6. The device as recited in claim 1, wherein theproximal slider includes a first length and the distal slider includes asecond length that is greater than the first length.
 7. An arthrodesisdevice, comprising: a nail body extending along a longitudinal axisbetween a proximal portion and a distal portion; a proximal interlockingfixation body slidably received within a first cannulation locatedinside the proximal portion; a distal interlocking fixation bodyslidably received within a second cannulation located inside the distalportion; and a shape memory material connecting member attached to theproximal interlocking fixation body and the distal interlocking fixationbody, wherein the shape memory material connecting member includes anelongated shaft extending between a first threaded portion and a secondthreaded portion.
 8. The device as recited in claim 7, wherein the nailbody includes at least one opening configured to receive a fixationdevice.
 9. The device as recited in claim 7, wherein a first opening islocated within the proximal portion of the nail body and receives atibial screw, a second opening is located within the distal portion ofthe nail body and receives a talar screw, and a third opening is locatedwithin the distal portion of the nail body and receives a calcanealscrew.
 10. The device as recited in claim 7, wherein the shape memorymaterial connecting member is a rod made of Nitinol (NiTi).
 11. Thedevice as recited in claim 7, wherein, when the nail body is implanted,the shape memory material connecting member is movable between anunstretched position and a stretched position to generate a compressiveforce across bones of a joint.
 12. An arthrodesis device, comprising: anail body extending along a longitudinal axis between a proximal portionand a distal portion; a proximal interlocking fixation body slidablyreceived within a first cannulation located inside the proximal portion;a distal interlocking fixation body slidably received within a secondcannulation located inside the distal portion; a shape memory materialconnecting member attached to the proximal interlocking fixation bodyand the distal interlocking fixation body; and a cable connected to thedistal interlocking fixation body, wherein the cable is tensioned tomove the distal interlocking fixation body inside the nail body.
 13. Amethod of performing an arthrodesis procedure, comprising: inserting anarthrodesis device within a joint; inserting a first fixation devicethrough the arthrodesis device; inserting a second fixation devicethrough the arthrodesis device; tensioning a cable of the arthrodesisdevice, wherein tensioning the cable alters a shape memory materialconnecting member of the arthrodesis device from an unstretchedcondition to a stretched condition; and releasing tension on the cable,wherein releasing the tension on the cable causes the shape memorymaterial connecting member to move back toward the unstretchedcondition, thereby applying a compressive load across bones of thejoint, wherein the shape memory material connecting member connectsbetween a proximal interlocking fixation body slidably received within afirst cannulation inside the arthrodesis device and a distalinterlocking fixation body slidably received within a second cannulationinside the arthrodesis device.
 14. The method as recited in claim 13,wherein the joint is a tibio-talo-calcaneal (TTC) joint of an ankle. 15.The method as recited in claim 13, comprising, prior to inserting thearthrodesis device: inserting a guide wire into the joint; and reaming apassage through the joint for accommodating the arthrodesis device. 16.The method as recited in claim 13, wherein the first fixation device iscalcaneal screw and the second fixation device is a tibial screw. 17.The method as recited in claim 16, comprising: inserting a thirdfixation device through the arthrodesis device after inserting thesecond fixation device, wherein the third fixation device is either atalar screw or a calcaneal screw.
 18. The method as recited in claim 13,wherein the cable is connected to the distal interlocking fixation body,wherein tensioning the cable includes: translating the distalinterlocking fixation body in a proximal to distal direction.
 19. Themethod as recited in claim 18, wherein translating the distalinterlocking fixation body moves the shape memory material connectingmember of the arthrodesis device from the unstretched condition to thestretched condition.
 20. The method as recited in claim 19, wherein theproximal interlocking fixation body is fixed from movement prior totensioning the cable.
 21. The method as recited in claim 19, whereininserting a third fixation device substantially locks a positioning ofthe distal interlocking fixation body.